Knockout Rose Tree

August 13th, 2011

For many many years roses were hybridized for fragrance, or hybridized for color, or for size. Things like hardiness and disease resistance were not as much of a concern. It is only recently that gardeners in general started worrying more about these more functional attributes. The “Knock Out” brand of rose is one such newer line that professes to be hardy and disease resistant.

I’ve been hearing about these for years, but never bought one. Then I got an offer from Brighter Blooms for a free plant (one of the benefits of being a garden blogger, you get swag). In particular they had a rose tree, and that really appealed to me.

A standard form plant is one in which a bush or weeping style plant has been either pruned, or more likely grafted, onto a standard (a trunk). Almost all weeping cherry trees sold are in fact standard form grafts, where a normal cherry is grown to the desired height, a weeping bud is grafted on, and then once it is established any regular cherry growth is pruned off.

So a rose tree isn’t a rose that genetically grows like a tree, it is just a rose shrub of one type of rose that has been grafted onto a strong trunk-like cane of another rose.

In anycase, to me the benefit of a standard form rose tree, was that it was easy to find room for it. I stuck it between two very large hardy hibiscus plants. The standard form provides height which provides separation. Had it been a normal shrub rose it would have been crowded by the hibiscus, it would have needed more room. In fact, if it had been a normal shrub, I would not have had room in my garden for it, anywhere. I’m really low on space, but the standard form allowed me to sneak it in there.

So I was all set to turn Brighter Blooms down, thinking I didn’t have any room, but then I saw the rose tree and thought “I could use one of those, and I’ll finally get a chance to checkout if “Knock Outs” are really all they are said to be. So I asked them for one, and a couple weeks later it arrived.

The tree arrived really well packed, the FEDEX driver couldn’t even fit it on my porch. It was an 8 foot box, seriously. Very strong double wall corrugated material, the tree is nowhere near 8 feet tall, but maybe that was the best sized box. In anycase, it definitely arrived safe, and full of blooms. Though it did bear a pesticide residue on the leaves that I mistook for powderly mildew, but I’m told the government requires the nursery to use it.

The blooms have petered out since then, just one on it now. Knockout roses are supposed to be “self cleaning” in that they do not need to be deadheaded to spur new blooms. I don’t know if I buy that. There were lots of hips (the rose fruit from a fertilized flower) forming. So I finally pruned them off. Roses do bloom in cycles, and it is on an off cycle now. But I didn’t see any “self cleaning” activity.,

It will of course take until next summer for me to assess hardiness. I am in zone 5, and they are supposed to be hardy to zone 5, but I worry about the tree. Grafts are notoriously weak points and often a grafted plant will die back to the graft, basically killing the plant. Now on a normal rose the graft would be way down at the ground level. With this one it is up higher, so more exposed to weather. That could prove decisive. I would feel safer in zone 6. But we will see.

I also hope to monitor disease resistance. I definitely normally get black spot and powdery mildew on my roses. Though some of my roses are obviously more disease resistant than others. You can have two roses right next to each other and one will rarely get badly infected, but the neighbor always will. So genetics do matter, and I’m hoping this tree will be the type that rarely is affected.

So next summer I will be doing a followup post on my overall impression of the Knock Out Rose’s performance.

I really like my Knock Out Rose bushes. My favorite is the yellow. The grow pretty vigorously and have required little attention. One even survived an attack by my dog and has managed to recover well. They are certainly much easier to care for than my fussy hybrid tea.

I just purchased 2 of these trees. My parents have the shrub variety and they are amazing! They are supposedly very heat and drought resistant and are also vety resistant to black spot and mildew. They are beautiful. Will be planting them tomorrow, wish me luck!

Not well Ben, most of the upper growth (95%) died over the winter. Now it is growing down from the roots, not from above the upper graft establishing the tree form. It is functionally dead as a tree. It wasn’t a cold winter either.

Thanks for posting this. I got an email advertising these trees that piqued my interest, and the site says they are hardy to zone 4. I was immediately skeptical and you confirmed my suspicions. About the only roses that can handle a Minnesota winter are those that are on their own roots with the crown slightly buried, plus protection. I won’t waste my time with anything with a graft too high to be covered. Too bad though, they are pretty.

I’ll tell you more Sarah, mine has since died back completely above the graft, and I don’t think it was winter either, it just wasted away, every year a few less canes above the graft, and now above the graft is completely gone and it is just putting out new canes from soil level.